Gas-blast circuit breaker of the recirculating gas type



Nov. 30, 1965 A. F. B. YOUNG 13,221,129

GAS-"BLAST CIRCUIT BREAKER OF THE RECIRCULATING GAS TYPE 1 .w u QQW e I m mam H s b M A 4 8m QM w 9 J k A/ i Q10. a w w n w 9 w m lNvENToR AUSTIN F. B YOUNG MMT Nov. 30, 1965 A. F. B. YOUNG 3,221,129

GAS-BLAST CIRCUIT BREAKER OF THE RECIRCULATING GAS TYPE 4 Sheets-Sheet 2 Filed April 28, 1961 Nm 3Q. KP Nu 3R .I ll Q m n J\%% j K m mwmw (w m R Q mu Q Q G R .MIGQ

lNVENTOR AUSTIN F B.YouN M1 4%, MwM

ATTORNEYS Nov. 30, 1965 A. F. B. YOUNG 3,22

GAS-BLAST CIRCUIT BREAKER OF THE REGIRCULATING GAS TYPE Filed April 28, 1961 4 Sheets-Sheet 5 v R F'" y v k I A A \Q 4 I m A Q j R [a a I m N 0 \r X Q N 5 i I I d i U R lNvENToR AusnN F B. YOUNG ATTQRN EYS Nov. 30, 1965 A. F. B. YOUNG 3,221,129

GAS-BLAST CIRCUIT BREAKER OF THE RECIRCULATING GAS TYPE 4 Sheets-Sheet 4.

Filed April 28, 1961 INVENTOR Ausrm F. BXoouG 4/ Y v Mil ATTQQNEY;

United States Patent 3,221,129 GAS-BLAST CIRCUIT BREAKER OF THE RECIRCULATING GAS TYPE Austin F. D. Young, Newcastle-on-Tyne, England, assignor to A. Reyrolle & Company Limited, Hebburn, England, a company of Great Britain Filed Apr. 28, 1961, Ser. No. 106,382 Claims priority, application Great Britain, Apr. 29, 1960, 15,245/60; Mar. 24, 1961, 10,971/61 Claims. (Cl. 200148) This invention relates to high-voltage gas-blast electric circuit-breakers of the type comprising a high-pressure gas container communicating through a blast valve with a low-pressure gas container which is at a pressure above atmospheric pressure and into which a blast of gas is delivered from the high-pressure container across an arc gap between a pair of circuit-breaking contacts separated on the opening of the blast valve, means being provided for pumping gas back into the high-pressure container to restore the pressure differential between the containers after the operation of the circuit-breaker.

According to the present invention, the low-pressure container is made of conducting material at the potential of the downstream circuit-breaking contact, the two contacts being electrically insulated from one another by solid insulation forming part of the wall of the highpressure container.

Thus the lowpressure container acts as a receptacle for the arcing products generated on operation of the circuit-breaker, and saves the solid insulation that electrically separates the circuit-breaking contacts from becoming contaminated by arcing products.

The invention in certain circumstances also obviates the need for using insulating pipes for pumping recycled gas back into the high-pressure container, since the inlet for the recycled gas can be formed in a part of the wall of the high-pressure container which is separated by insulation atfording full voltage clearance from the upstream circuit-breaking contact and its associated live parts. In such cases the pipe or pipes interconnecting the pump to the high-pressure container may be made of metal. The pump itself will then be at the voltage of the downstream contact of the circuit-breaker.

Preferably the ratio of the gas pressure in the highpressure container to that in the low-pressure container should be in the region of 4: 1, and not greater than 5:1, this limiting ratio being within the capacity of a singlestage pump for returning the gas from the low-pressure to the high-pressure container, whilst yet allowing several operations of the circuit-breaker in rapid succession without pumping before the pressure ratio falls below the minimum value required to produce a gas blast at supersonic velocity across the arc gap.

Where the arc-extinguishing gas used in the circuitbreaker is air, the pressure maintained in the low-pressure container should preferably be not less than 100 lbs. per square inch gauge, so that the compressed air around the arc will have a high electric strength and also so that the volume of the containers can be kept small. However, the use of other and more expensive arc-extinguishing gases having better electrical properties than air, for example one of the electro-negative gases such as Freon, is within the scope of the invention and would enable "ice lower pressures to be maintained in the containers without detriment to the arc-extinguishing capacity of the circuit-breaker and with economy in construction.

A further feature of the invention is that it enables the compressed gas used for extinguishing the arc to be entirely segregated, if required, from the solid and gaseous insulants supporting and enclosing the arc-extinguishing unit as a whole, although it will be understood that the invention is not restricted to such entirely segregated arrangements. These arrangements employ a sealed-gas blast system and avoid the discharge of high velocity streams of hot gases contaminated with arcing products into the atmosphere around the circuit-breaking unit, so that the risk of mixing and flash-over between the exhausts of adjacent interrupting units is avoided and quieter operation is obtainable, thus making the circuitbreaker suitable for indoor or outdoor use.

Thus according to a further feature of the invention the high and low-pressure chambers of the circuit-breaker may be housed in an outer vessel containing insulating gas at a low superatmospheric pressure, for example lbs. per square inch. The circuit-breaker may incorporate a wholly sealed circulation system for the arc-extinguishing gas comprising a pump directly connected by pipes between the low-pressure container and the high-pressure container.

In another arrangement of the invention in which the circuit-breaker is enclosed in an outer vessel containing gas at a pressure above atmospheric pressure, the gas pressure in the outer vessel may be equal to that in the low-pressure container, and the interior of the low-pressure container may communicate through a gas filter and cooler with the interior of the outer vessel outside the low-pressure container, means being provided for pumping gas from within the outer vessel into the high-pressure container to restore the pressure ditferential between the two containers after operation of the circuit-breaker.

In one such arrangement the pump is mounted outside the outer vessel with its inlet connected to a port in the wall of the outer vessel and with its outlet connected via a passage passing through the wall of the outer vessel to the inlet of the high-pressure container, at least theinner end of the said passage being defined by a conduit of insulating material.

The invention may be carried into practice in various ways but three specific embodiments will now be described by way of example only with reference to the accompanying drawings, in which:

FIGURE 1 is a diagrammatic view of a single-break live-tank gas-blast circuit-breaker embodying the invention,

FIGURE 1A is a diagrammatic view showing in detail a portion of the circuit-breaker shown in FIGURE 1.

FIGURE 2 is a diagram of a two-break live-tank circuit-breaker mounted on a single insulating post,

FIGURE 3 is a diagrammatic sectional view of a fourbreak dead-tank circuit-breaker,

FIGURE 4 is a view similar to FIGURE 3 of a modified form of four-break deak-tank circuit-breaker, and

FIGURE 5 is a sectional view of another modified construction of four-break dead-tank circuit breaker.

In the embodiment of FIGURE 1, a single-break livetank circuit-breaker having a sealed arc-extinguishing gas system includes an arc-interrupting unit 10 comprising a pair of axially aligned cylindrical containers 11 and 12 having a common end wall 13 in which is formed a nozzle 14 for the gas-blast. The upstream container 11 is filled with compressed air at about 500 lbs. per square inch and constitutes the high-pressure container, having a cylindrical insulating wall 15 secured at one end to the common end wall 13 and carrying at its other end a metal end cap 16 which carries one terminal 17 of the interrupting unit 10. An elongated conductor 18 mounted at its outer end on the end cap 16 extends coaxially within the high pressure container 11 towards the nozzle 14, the inner end 19 of the conductor 18 constituting the fixed circuit-breaking contact of the circuit-breaker and being spaced a short distance from the nozzle 14. The conductor 18 is electrically connected by the metal end cap 16 to the associated terminal 17 of the unit 10.

The other or low-pressure container 12 is made wholly of metal and houses the moving contact 21, which comprises a longitudinally withdrawable rod extending coaxially within the container 12 with its inner end normally protruding through the nozzle 14 into electrical contact with the fixed circuit-breaking contact 19. The outer end 22 of the moving contact rod 21 protrudes out through the end wall 23 of the low-pressure container 12, being sealed by means of a bellows-type seal 24, and is connected to a mechanical drive mechanism 25 by means of which it can be withdrawn longitudinally to draw an are between its inner end and the fixed contact 19, the arc standing through the nozzle 14 as indicated at 27 as the moving contact 21 is withdrawn clear of the nozzle 14.

The low-pressure container 12 also houses a blast-valve 30 and an annular cooler for the hot gas-blast, and is itself maintained at a pressure of 150 lbs. per square inch gauge downstream of the blast valve 30. Thus, secured within the outer cylindrical wall of the container 12 is a cylindrical metal cooler liner 31 defining an annular cooler passage 32 closed at its end nearest the common end wall 13 and open at its other or downstream end as indicated at 33. An inner cooler battle wall 34, also in the form of a cylindrical metal skirt, extends coaxially within the liner 31 from the outer end wall 23 of the container 12 to define a second annular cooler passage 35 communicating at 33 with the open downstream end of the first passage 32, and opening at its other end into the interior of the container 12 within the bafiie wall 34. A series of blast ports 36 are formed in a ring around the metal liner 31 near the common end wall 13 for co-operation with the blast valve 30, the blast ports 36 being separated from the region within the cooler 31, 34 by a conical metal barrier 37 secured at its periphery to the liner 31, the barrier 37 defining with the common end wall 13 a conical passage 38 leading from the nozzle 14 to the blast ports 36. This conical passage 38 is normally maintained at the pressure of the high-pressure container 11 by means of the blast-valve 30, which comprises a cylindrical valve sleeve surrounding the metal liner 31 and normally covering the blast ports 36. The blast Valve sleeve 30 is coupled to the drive mechanism 25 by means of a rod 30A connected to an arm 30B mounted on the outer end 22 of the moving contact rod 21, in such a manner that when the moving contact rod 21 is withdrawn from the fixed contact 19 to draw an arc at 27, the blast valve sleeve 30 is withdrawn to uncover the blast ports 36 as indicated in FIGURE 1, so that a blast of compressed air is initiated to flow at supersonic velocity through the nozzle 14. The blast scours the arc as it stands through the nozzle at 27 and carries the arcing products along the conical passage 38, through the open blast ports 36, along the outer passage 32 of the cooler, thence in the reverse direction along the inner passage 35 of the cooler, until they emerge, cooled and if necessary filtered, into the interior of the container 12 Within the baffle wall 34. The moving contact rod 21 extends through a central close-fitting aperture at 39 in i the conical barrier 37 and is not withdrawn beyond the barrier 37.

For restoring the pressure diiferential between the highpressure and low-pressure containers 11 and 12, a singlestage pump 40 is provided, connected by metal pipes 41 and 42 between an outlet port 43 provided in the end wall 23 of the low-pressure container 12 and an inlet port 44 formed in the insulating wall 15 of the high-pressure container 11 close to the common end wall 13. It will be understood that with this arrangement the pump itself and the metal connecting pipes are alive, being at the voltage of the downstream terminal 45 of the interrupter unit 10. The pump 40 is driven by an insulating mechanical drive 46. Similarly an insulating connecting rod 47 is provided for transmitting the operating drive to the drive mechanism 25 for the purpose of withdrawing the moving contact rod 21 and the blast valve sleeve 30 to operate the circuit-breaker. The whole interrupter unit 10 is supported by a single post insulator 48 on the head of which the metal low-pressure container 12 is mounted, the unit 10 being itself in atmospheric air.

FIGURE 2 shows diagrammatically a two-break circuitbreaker comprising a pair of interrupting units each generally similar to the unit 10 of FIGURE 1, each unit having a separate high-pressure container 50 but the two units sharing a common low-pressure container 51 mounted on a single insulating post 52. The two high-pressure containers 50 project outwardly in opposite directions from the two ends of the common low-pressure container 51 so that their metal end caps 53 and 54 atford the terminals of the circuit-breaker. The main parts of the two high-pressure containers 50 are afforded by cylindrical insulating walls which, as in the case of FIGURE 1, are disposed upstream of the nozzles through which the two series arcs are drawn on operation of the circuit-breaker. A single pump is provided for restoring the gas-pressure differential between the highpressure containers 5t and the common low-pressure container 51, the pump having an insulating drive which, together with the drive for the operating mechanism of the two interrupting heads, extends through the support insulator 52.

The embodiment of FIGURE 3 comprises a four-break dead-tank construction of circuit-breaker made up of two similar back-to-back two-break combinations generally as described with reference to FIGURE 2, and connected together in series. Thus in the arrangement of FIGURE 3 each two-break interruptor combination comprises a common low-pressure container on the ends of which are mounted two high-pressure containers 61 and 62 whose side walls are of insulating material. Each outer high-pressure container 61 carries a metal end cap 63 whilst the two adjacent inner high-pressure containers 62 are joined together end-to-end and share a common insulating wall. The arrangements of circuitinterrupting contacts, nozzles and blast valves of the four interrupting units in this combination are generally similar to those of FIGURES 1 and 2 and are illustrated diagrammatically only in FIGURE 3. Thus the four fixed contacts in the high-pressure containers 61 and 62 are shown at 65, and the movable contacts 66 normally extend through nozzles 67 into electrical contact with the fixed contacts but are withdrawable inwardly by suitable retraction means 68, for example of the rack and pinion type, operated by an insulating mechanical drive 69. The two two-break interrupter combinations described and illustrated are electrically connected together in series, with the outer high-pressure containers 61 supported from the lower ends of two insulating lead-in bushings 71 which extend into an earthed metal tank 70 in which the interrupting units are contained, the conductors of the bushings 71 being connected to the end caps 63. The tank 70 is filled with insulating fluid, which may be liquid or compressed gas. Where this insulating fiuid is air, it is at a pressure lower than the gas-pressure in the low-pressure containers 60, for example 50 lbs. per square inch. Two pumps 72 are mounted outside the interrupter units in the interior of the tank 70, and are connected to metal pipes 73, 73A the inlet of each pump 72 being connected by a pipe 73 to one of the low-pressure containers 60 and its discharge outlet being connected to the two associated high-pressure containers 61 and 62 into which the pipes 73 lead through inlet ports in the insulating walls of the high-pressure containers in the manner described with reference to FIGURE 1. Thus the insulating fluid in the tank 70 is wholly segregated from the sealed systems of arc-extinguishing gas contained within the high and low-pressure containers of the interrupter units and their associated pumps and pump connectors. An insulating drive 74 for the two pumps 72 extends into the earthed tank 70.

If segregation of the insulating fluid in the tank 70 from the arc-extinguishing fluid within the interrupter units is not required, it is possible for the earthed metal tank 70 to be filled with compressed air at 500 lbs. per square inch in direct communication with the interiors of the high-pressure containers of the interrupting units. One such arrangement is illustrated in FIGURE 4, in which the same reference numerals as in FIGURE 3 are used for similar parts. In this case, however, the pumps 72 have their inlets connected by the pipe 73 to ports in the Walls of the two low-pressure containers 60, but discharge directly into the interior of the tank 70. High-pressure gas from the interior of the tank 70 can enter the high-pressure chambers 61 and 62 through ports 75 in the insulating walls of the chambers 61 and 62 to restore the gas pressure within the chambers 61 and 62 to that of the gas surrounding them within the tank 70, after the operation of the circuit-breaker. This arrangement may not be suitable for use in cases where the gas contained in the tank 70 is liable to deterioration of its insulation properties when subjected to electrical arcing, as happens in the case of certain insulating gases other than air which undergo chemical changes when subject to arcing.

FIGURE 5 illustrates another embodiment of the invention in which the arc-extinguishing gas system is not segregated from the main insulating fluid within the earthed outer tank. In the embodiment of FIGURE 5 a four-break circuit-breaker is provided which comprises, as before, a back-to-back combination of two two-break interrupting units, and is housed in an outer earthed metal tank 80 filled with compressed air at pressure above atmospheric pressure, for example 100 lbs. per square inch. Each two-break interrupter unit comprises a common high-pressure container 81 having a cylindrical wall of insulating material, and having an outer low-pressure container 82 mounted at one end and an inner low-pressure container 83 mounted at its other end. The two inner low-pressure containers 83 share a common cylindrical metal side wall 84 and are closed by domed convex metal end walls 85 facing into the adjacent common high-pressure container 81. Similarly each outer low-pressure container 82 has a domed convex metal end wall 85 protruding into the interior of the high-pressure chamber 81.

The back-to-back assembly of chambers is mounted within the tank 80 by means of two lead-in bushings 86 the lower ends of whose conductors are mechanically and electrically connected at 87 to the outer low-pressure containers 82. In addition a high-pressure reservoir 88 of earthed metal mounted on the exterior of the tank 80 communicates via an insulating tube 89 with the two highpressure chambers 81 so that the interiors of each highpressure chamber 81, of the tube 89 and of the reservoir 88 are at a common high gas pressure, say 500 lbs. per square inch, and effectively constitute a single volume filled with high-pressure gas. In this way the effective volume of each high-pressure chamber 81 is increased by half the volumes of the reservoir 88 and tube 89, so that the volume of each high-pressure chamber 81 need itself be suflicient only for a single current interruption.

The domed metal end walls of the low-pressure containers, by their protrusion into the interiors of the two high-pressure containers 81, also effect an increase of the volumes of the low-pressure containers by allowing them to encroach axially into the adjacent high-pressure containers, without increasing the overall axial length of the assembly. Thus for a required minimum volume each lowpressure container 82 or 83 can be made axially shorter than would otherwise be possible. In addition the domed convex shapes of the end walls 85 of the low-pressure chambers exhibit a configuration which produces a beneficial distribution of electric stress between the two ends of each high-pressure chamber, as well as imparting additional mechanical strength to them for resisting the gas pressure differential.

A single earthed pump 90 mounted outside the tank 80 is connected by metal pipes 91 and 92 respectively between an outlet port 93 in the metal wall of the tank 80 and an inlet port 94 in the wall of the high-pressure reservoir 88, the pump being employed to pump gas from the interior of the tank 80 into the interior of the high-pressure reservoir after a circuit-breaker operation to restore and maintain the required gas pressure differential.

An elongated drive shaft 96 extends along the interior of the four-break interrupting assembly, passing outside the four low-pressure chambers 82 and 83 but inside the two high-pressure chamber 81 as indicated. The driving shaft 96 is driven through bevel gearing 97 by an insulating transverse driving shaft 98 extending coaxially within the insulating tube 89, the shaft 98 being itself driven through bevel gearing 99 by a shaft 100 in the high-pressure reservoir 88. Since the reservoir 88 is at earth potential the shaft 100 can be connected directly to the pneumatic or other circuit-breaker operating means. The insulating driving shaft 96 carries two sets of bevel gearing 101, only one of which is visible in FIGURE 5, and each of which drives an insulating spindle 102 extending across each high-pressure chamber 81, each spindle 102 carrying a pinion 103 which co-operates with rack means 104 by which two movable arc-interrupting contacts 105 can be advanced or withdrawn longitudinally.

Each movable contact 105 co-operates with a fixed contact 106 afforded by the rim of a nozzle aperture 107 formed in the domed end wall 85 of the associated lowpressure chamber 82 or 83. Downstream of each nozzle aperture 107 the metal of each domed wall 85 is extended to form a generally conical nozzle 108, at the inner end of which is provided a valve seating 109 with which cooperates a movable blast valve member 110 carried on one end of a piston rod 111. Each blast valve 109, 110 is operated pneumatically under the control of a pilot valve 112 which controls the admission of high-pressure gas from the chamber 81 into an inlet port 113 in the wall of the associated low-pressure chamber 82 or 83, the inlet port 113 leading via a conduit 114 to a cylinder 115 formed within each of the low-presure chambers 82 and 83. A piston 116 mounted on the other end of the piston rod 111 fits within the cylinder 115, so that when highpressure gas is admitted by the pilot valve 112 into the cylinder 115 it acts on the piston 116 to lift the blast valve member 110 from its seating 109 and so to initiate a blast of arc-extinguishing gas from the high-pressure chamber 81 through the nozzle 107 into the low-pressure chamber 82 or 83.

It will be observed that the two central low-pressure chamber 83 which are contained within a single metal side wall 84 share a single cylinder 115, in which are two pistons 116 arranged back-to-back and respectively associated with the two blast valves. However the outer lowpressure containers 82 each have only a single piston in the actuating cylinder, by which the associated blast valve is operated.

The operation of the various blast valves is also initiated by the rotation of the driving shaft 96, which carries three rotary cams 118 (only one of which is visible in FIGURE which respectively co-operate with cam followers 119 on the spindles of the pilot valves 112, so that the rotation of the shaft 96 in one direction causes each pilot valve 112 to be opened to admit compressed gas to the associated cylinder 115, and further rotation of the shaft 96 closes the valve 112 to cut off communication between the high-pressure container 81 and each cylinder 115 but connects each cylinder 115 to a dump passage shown diagrammatically at 120 and leading out through the wall of the high-pressure chamber 82 into the interior of the outer tank 80, which as already stated in normally maintained at the same low pressure as the low-pressure chambers 82 and 83, for example 100 lbs. per square inch in the case Where air is used as the compressed gas.

Mounted in the interior of each of the low-pressure chambers 82 and 83 is a gas cooler of the labyrinth type afforded by a series of overlapping annular sheet metal baflies 122, which as indicated provide an elongated path for the passage of hot gases from the blast valve to the region 123 of each low-pressure chamber 82 or 83, when the blast valve is opened. Thus the hot gases escaping through the cooler will be cooled by contact with the cooling surfaces afforded by the metal baflies 122 before reaching the region 123.

Moreover a filter 124 is mounted in an aperture in the side wall of each of the low-pressure chambers 82 and 83 so as to afford communication between the regions 123 of the low-pressure chambers and the interior region 125 of the outer earthed metal tank 80 outside the chambers, and to filter gases caused to pass outwardly from the chamber 82 or 83 into the region 125 by a gas pressure differential.

Thus the operation of the circuit-breaker of FIGURE 5 is as follows. When the circuit-breaker is closed, the four movable contacts 105 are in contact with the fixed contacts 106. The four blast valve members 110 are closed onto their seatings 109 and the three pilot valves 112 are closed. On the occurrence of a fault in the systern protected by the circuit-breaker, the circuit-breaker is tripped and the driving mechanism 100, 99, 98, 97, and 96 is operated. This rotation of the elongated driving shaft 96 causes rotation of the two spindles 102 to retract the four movable contacts 105 from their associated fixed contacts 106, thereby drawing arcs in the four are gaps thus produced. Simultaneously, and before the circuit-breaking contacts 105 and 106 have separated, the rotation of the three cams 118 opens the three pilot valves 112, admitting high-pressure compressed gas to the cylinders 115 to act on the pistons 116 and thereby opening the four blast valves 110. This initiates a blast of arcextinguishing gas to flow through each nozzle aperture 107 from the associated high-pressure chamber 81 into the passage within the conical nozzle 108, and thence through the opened blast valve 109, 110, into the associated low-pressure chamber 82 or 83. The blast of arcextinguishing gas through each nozzle 107 scours the arc until eventually the arc is extinguished, the hot ionised products of arcing being carried by the blast through the nozzle apertures 107 and into the associated low-pressure chambers 82 and 83 in which they are cooled and de-ionised by contact with the annular cooling surfaces 122 of the cooler. The cooled and de-ionised blast eventually emerges into the region 123 of each low-pressure chamber 82 or 83, causing a rise of gas pressure in that chamber. The resultant pressure differential across the filters 124 causes gas to trickle slowly out through the filter into the interior region 125 of the earthed metal tank 80 outside the high and low-pressure chambers, to mingle with the gas already contained in the region 125 of the tank 80.

After arc extinction, further rotation of the driving shaft 96 closes the blast valves by causing the pilot valves 112 to dump the high-pressure in the cylinders 115. When the gas pressure in the high-pressure chambers 81, and in the reservoir 88, has been reduced by one or more operations of the circuit-breaker to a value below that required in relation to the pressure in the tank and in the low-pressure chambers, the pump is automatically operated to pump gas back from the tank 80 at low pressure into the reservoir 88 at high pressure, until the pressure differential is restored.

To reclose the circuit-breaker the shaft 96 is rotated by the driving means in the opposite direction.

What I claim is:

1. A high voltage gas-blast electric circuit-breaker comprising an outer vessel, a high-pressure gas container and a low-pressure gas container within said outer vessel, the gas pressure in said outer vessel and said low-pressure gas container normally being equal and above atmospheric pressure, said high-pressure gas container communicating with said low-pressure gas container through a blast valve, said low-pressure container communicating with said outer vessel through a cooler, circuit-breaking contacts positioned within said high pressure container and electrically insulated from one another by solid insulation forming part of the wall of the high-pressure container, said low-pressure container being of conducting material at the potential of one of the circuit-breaking contacts, means for simultaneously opening said blast valve and separating said contacts whereby a blast of gas is delivered from said high-pressure container across an air gap between said circuit-breaking contacts to said low pressure container and through said cooler to said outer vessel whereby the pressure is equalized, and means for pumping gas from said outer vessel back into the highpressure container to restore the pressure differential between said two containers after the operation of the ciromit-breaker.

2. A high-voltage gas-blast electric circuit-breaker which comprises an interrupter unit having a high-pressure gas container constituting a reservoir of compressed arc-extinguishing gas at high pressure, a low-pressure gas container constituting a receiver vessel maintained at a low gas pressure above atmospheric pressure, separable circuit-interrupting contacts positioned within said high pressure container, and a blast valve which when opened provides communication between the high-pressure reservoir and low-pressure receiver vessel to cause a blast of gas to be delivered from the high-pressure reservoir across an arc gap between the separated contacts into the lowpressure receiver vessel, said circuit-breaker also including an outer vessel at earth potential containing arc-extinguishing gas at a low pressure above atmospheric pressure, in which outer vessel the interrupter unit is housed, pumping means for pumping gas from the interior of the outer vessel into the high-pressure receiver after each operation of the circuit-breaker, said low-pressure receiver vessel being provided with a gas cooler communicating with said outer vessel whereby a restricted gas flow is permitted from the interior of the low-pressure receiver into the surrounding interior of the earthed outer vessel through the cooler.

3. A circuit-breaker as claimed in claim 1 in Which the pumping means comprises a pump mounted outside the outer vessel with its inlet connected to a port in the wall of the outer vessel and with its outlet connected by a delivery passage extending through the wall of the outer vessel to an inlet to the high-pressure container, at least the downstream part of the delivery passage being afforded by an insulating conduit.

4. A circuit-breaker as claimed in claim 1 in which the high-pressure container and the low-pressure container share a common end wall of domed shape which protrudes into the interior of the high-pressure container.

5. A circuit-breaker as claimed in claim 4 which comprises a double-break circuit-breaker including a back-toback arrangement of two low-pressure containers having 9 a common high-pressure container between them, and in which the two end walls of the high pressure container which are common to the respective low-pressure containers are of domed form protruding into the interior of the high-pressure container.

References Cited by the Examiner UNITED STATES PATENTS 2,108,560 2/1938 Kesselring 200-148 2,673,271 3/1954 Amer 200-148 2,757,261 7/1956 Lingal et a1. 200148 2,772,335 11/1956 Hidde Nijland 200-148 2,955,182 10/1060 Caswell et a1 200148 KATHLEEN H. CLAFFY, Primary Examiner.

MAX L. LEVY, BERNARD A. GILHEANY, Examiners. 

1. A HIGH VOLTAGE GAS-BLAST ELECTRIC CIRCUIT-BREAKER COMPRISING AN OUTER VESSEL, A HIGH-PRESSURE GAS CONTAINER AND A LOW-PRESSURE GAS CONTAINER WITHIN SAID OUTER VESSEL, THE GAS PRESSURE IN SAID OUTER VESSEL AND SAID LOW-PRESSURE GAS CONTAINER NORMALLY BEING EQUAL AND ABOVE ATMOSPHERIC PRESSURE, SAID HIGH-PRESSURE GAS CONTAINER COMMUNICATING WITH SAID LOW-PRESSURE GAS CONTAINER THROUGH A BLAST VALVE, SAID LOW-PRESSURE CONTAINER COMMUNICATING WITH SAID OUTER VESSEL THROUGH A COOLER, CIRCUIT-BREAKING CONTACTS POSITIONED WITHIN SAID HIGH PRESSURE CONTAINER AND ELECTRICALLY INSULATED FROM ONE ANOTHER BY SOLID INSULATION FORMING PART OF THE WALL OF THE HIGH-PRESSURE CONTAINER, SAID LOW-PRESSURE CONTAINER BEING OF CONDUCTING MATERIAL AT THE POTENTIAL OF ONE OF THE CIRCUIT-BREAKING CONTACTS, MEANS FOR SIMULTANEOUSLY OPENING SAID BLAST VALVE AND SEPARATING SAID CONTACTS WHEREBY A BLAST OF GAS IS DELIVERED FROM SAID HIGH-PRESSURE CONTAINER ACROSS AN AIR GAP BETWEEN SAID CIRCUIT-BREAKING CONTACTS TO SAID LOW PRESSURE CONTAINER AND THROUGH SAID COOLER TO SAID OUTER VESSEL WHEREBY THE PRESSURE IS EQUALIZED, AND MEANS FOR PUMPING GAS FROM SAID OUTER VESSEL BACK INTO THE HIGHPRESSURE CONTAINER TO RESTORE THE PRESSURE DIFFERENTIAL BETWEEN SAID TWO CONTAINERS AFTER THE OPERATION OF THE CIRCUIT-BREAKER. 